1. Field of the Invention
This invention relates to formation of ultra low k films and to reagents suitable for such use.
2. Description of the Related Art
A wide variety of reagents are actively being investigated for use in forming ultra low dielectric constant (k) films on substrates, in connection with development of next generation microelectronic devices. As used herein, the term “ultra low dielectric constant” refers to a dielectric constant below 2.
In continuing efforts to reduce k values of thin films in microelectronic device fabrication, various compositions involving porosity-forming reagents, i.e., porogens, have been developed. By generating porosity in the dielectric film, the void volume (having a dielectric constant of ˜1) contributes to an overall lowering of the dielectric constant of the film containing such porosity.
Many organics have been considered for use as pore generators. Among them, bicyclo[2.2.1]-hepta-2,5-diene (BCHD) is a promising candidate, however, its use for forming dielectric constant films requires that the material be of very high purity. High purity BCHD, however, can be unstable, and readily polymerizes. This in turn creates the possibility of clogging of reagent delivery lines in the semiconductor process system, and of unwanted polymerization deposits in the deposition chamber.
Diethoxymethylsilane (DMS) is used as a precursor for plasma-enhanced chemical vapor deposition (PECVD) of ultra low k films. However, DMS is susceptible to polymerization and resultant clogging behavior in the delivery lines of the process system.
The art has a continuing need for improved porogen and precursor materials for forming ultra low k dielectric films.